The present invention relates to vehicle fluid suspension systems, and more particularly to a control system for selectively controlling the components of a fluid suspension system.
Fluid suspension systems are well known for providing a softer, more comfortable ride for a vehicle. Other common applications for fluid suspension systems include: raising or lowering a vehicle; leveling a vehicle that is under a load; leveling recreational vehicles parked on inclined surfaces; and altering the performance characteristics of a vehicle. Fluid suspension systems may be installed on a vehicle by the original equipment manufacturer, or they may be purchased as aftermarket products that are substitutes or supplements for conventional steel spring suspensions.
Common fluid suspension systems may include one or more pneumatic devices, such as air springs, connected between the vehicle axles and the vehicle chassis. Pressurized air from an air supply can be forced into or exhausted from one or more of the air springs to provide the vehicle with desired suspension characteristics.
Some air suspension systems are connected to control systems that automatically force air into the air springs or exhaust air from the air springs upon certain conditions. For example, many vehicles are equipped with a ride height control system that utilizes height sensors or pressure sensors in combination with a controller to monitor the relative height of the vehicle in one or more locations, and automatically supply or exhaust fluid from one or more air spring as a function of the sensor output. In a similar manner, it is common for recreational vehicles to include automatic leveling systems that utilize similar height or pressure sensors to level a vehicle, for instance, when the vehicle has been parked in a desired parking space.
In public buses and emergency vehicles, it is common for control systems to operate fluid suspension systems that lower portions of the vehicle for selected periods of time—often referred to as “kneeling”—in order to make the vehicle more accessible to users. Buses often kneel by lowering an air spring nearest to the door of the bus when the bus is stopped to allow passengers to enter and exit, such that the landing is closer to the street for easier ingress and egress by the passengers.
In emergency vehicles, the kneel function is commonly located at the rear of the vehicle, such that the rear can be raised and lowered to enable wheeled stretchers to be moved into and out of the rear doors of the emergency vehicle. One known control system for operating the kneel function in an emergency vehicle includes a kneel switch triggered by the opening or closing of the rear door. In one known configuration, the control system exhausts the air springs each time the rear door is opened to lower the rear of the vehicle to an appropriate height to access the vehicle. Each time the rear doors are closed, the kneel switch triggers the control system to fill the air springs such that they raise the vehicle to an appropriate ride height.
Unfortunately, this type of emergency vehicle control system often leads to unnecessary raising and lowering of the vehicle. For example, typical operation of emergency vehicles includes: (1) parking the vehicle, (2) opening the rear doors to unload the stretcher, (3) closing the rear doors, (4) opening the rear doors again to load the stretcher, and (5) closing the rear doors again before driving away. In some cases, the doors are opened and closed additional times in order to remove additional equipment. Each opening and closing of the rear doors causes the control system to raise or lower the rear air springs, regardless of whether or not the stretcher is being loaded or unloaded.